The present invention relates to an automotive vehicle speed control system such as a steady-speed driving system, or more in particular, to an automotive vehicle speed control system comprising signal generating means for processing a speed signal representing the actual running speed of the automotive vehicle and a target signal representing a target running speed of the vehicle, thereby to actuate a speed control element of the vehicle, and generating a speed-up command signal, and transient control means for increasing the running speed of the vehicle on the basis of the command signal thus generated.
An automotive vehicle speed control system comprising this transient control means is well known as disclosed in Japanese Patent Laid-Open Publication No. 86539/82, which suggests a system of increasing the target signal by a predetermined value while an operating switch is on, in response to an operation signal of the operating switch controlled by the driver.
In the prior art, the target signal is always set above the actual running speed by a certain value while the operating switch is operated, and therefore, the target signal increases slowly on an uphill road where the actual acceleration is small, whereas the target signal increases sharply on a downhill road, resulting in an unstable riding quality. Further, a problem exists in that when the operation of the operating switch is cancelled, the running speed is not maintained at a target value immediately but an overshoot is caused.
The problem pointed out above is also likely to be posed in a control system in which after the automatic speed control mode is cancelled, the automatic speed control mode is capable of being restored by operating another operating switch.